Use `#160` instead of `nbsp` for unlabeled nodes.
Use `#160` instead of `nbsp` for unlabeled nodes.

Otherwise any tree with such nodes will fail when exporting/downloading
as SVG (which doesn't recognize most mnemonic HTML entities).

OpenTreeOfLife/opentree,OpenTreeOfLife/opentree,OpenTreeOfLife/opentree,OpenTreeOfLife/opentree,OpenTreeOfLife/opentree,OpenTreeOfLife/opentree